When unmarried couples live together for a while, it is likely that they accumulate a good amount of property. In this case, it is in each person's best interest to write out a property agreement that spells out who owns what and how the property will be distributed should the couple separate. Without an agreement, you could face expensive and time consuming legal battles, defending your property rights. This trouble can be saved by each party entering an agreement they both consent to, while the relationship is sound.